Just about every manufacturer seems to use a different way of labeling motors. Some places the first two numbers are the outer can diamiter, no idea what the second two do, then generally the dash means how many turns the motor has.

But, like I said, none of them really mean the same thing.

The constants I've noticed, is about 100watts per ounce, and compare kv ratings to get an idea of speed and voltage.

The kv rating tells you how many rpm's you get per volt, which will give you a general idea of prop size by cell count.

For the TP motors the 24=stator diameter, 10=stator length, 8=turns.
You have to know motors to realize that it's a delta termination to get the 890kv. Star termination of the same motor winding would give it a kv- ~1500.

The specs you see in HK are outside measurements. Some motors do indeed only use outside measurements.

For SOME motors, IF YOU KNOW, you can decipher some of the info. For a lot of them...it means nothing at all. On top of that the specs are often only ballpark because the QA is so poor (like the TP motors) that specs are only approximate anyway. The cheaper the motor, likely the worse the QA.
You really NEED to measure the output with a wattmeter.

fly
If you're going to learn to fly them, you have to learn to fix them.

My experience with the Hobby King motorsm for example, has shown significant variances. I have had DOA that would have cost more to have corrected than the cost of the motor. Delayed a build as I waited a month for the motor and it was no good.

My experience with the Tower Hobbies and Great Planes Rimfire motors are that they are very good and true to specs. And the info available is excellent. My preferred brand.http://www.electrifly.com/motorsgears.html

You pay more for the Great Planes motors but you get the quality and support. And Tower ships fast.

Of course your smileage will vary. I can only reflect on my experience.

One reason why I like heads up rc, they give you just about every dimension imaginable for most motors, as well as actual testing, prop thrust and amprage under load. Even at my 4500ft elevation, his numbers have been spot on for everything I've ordered. I almost always run a combo with the maximum recommended specs, and haven't had a single failure.

Some electric motors are even named for the glow motor they would replace. e-Flite likes to do that.

Which is meaningless to a whole generation of us that have never flown glow. Near as I can tell by all the questions it doesn't much help the glow guys either because they don't know squat about electric (which prop/ESC/battery should I get?).

fly
If you're going to learn to fly them, you have to learn to fix them.

Especially where there are many different kinds of .40 glow engines, that could be a completely different motor depending on cell count and prop size. Even from a 3-4 cell you can double power output without severly effecting amprage or even thrust. It just takes some time and effort.

Once again, why I like heads up. Some 480 class motors could replace anything from a .10, to a .25 glow engine. The kv rating also really effects what size prop you can safely use. Not too many .40 planes have prop clearance for more then a 10" prop, but with some electrics, you can easily get from a 8" all the way to a 14 or even 15" prop, depending on cell count.

One thing about Heads Up--they don't just print the manufacturer supplied numbers. They test the product and give you real world figures for different prop combinations for your motor from their test results. It's information you can actually rely on.

Usually we pay a premium price for good information. With Heads Up its just the way they do business.